ON  ZINC  SULPHO-PHENATE. 
137 
days  the  combination  is  accomplished,  and  the  mixture  is  then 
diluted  with  ten  times  its  bulk  of  water.  Now  twice  as  much  as 
the  quantity  of  sulphuric  acid  operated  upon,  or  better,  a  little 
more,  of  dry  barium  carbonate,  is  gradually  added  (to  120  parts 
(h  S,'  245  parts  Ba  o).  The  latter  had  better  be  triturated  with, 
some  water  before  it  is  added  to  the  acid.  Under  evolution  of 
carbonic  acid  barium  sulpho  phenate  is  formed,  a  salt  soluble  in 
water  and  in  alcohol.  At  the  same  time  any  excess  of  free  sul- 
phuric acid  is  neutralized  and  transformed  into  barium  sulphate. 
The  whole  is  allowed  to  stand  in  a  warm  place  for  some  hours, 
and  is  then  filtered  through  a  damp  filter  ;  the  remainder  on  the 
filter  is  washed  with  some  warm  water.  The  filtered  solution  of 
barium  sulpho-phenate  may  be  evaporated  to  dryness,  whereby 
it  remains  behind  as  a  white  salt  deprived  of  its  water  of  crystal- 
lization. This  is  soluble  in  two  parts  of  water.  A  small  quantity  of 
this  barium  salt  is  retained,  the  balance  is  dissolved  in  water  in  the 
proportion  of  10  parts  of  the  first  to  30 — 40  parts  of  the  latter. 
To  this  filtered  solution  a  solution  of  6  parts  crystallized  zinc- 
sulphate  in  about  18  parts  of  water  is  added.  Of  this  zinc  so- 
lution a  small  quantity  is  also  retained.  Now,  after  leaving  the 
mixture  on  the  water  bath  for  several  hours,  about  10  drops  of 
the  supernatant  solution  are  diluted  in  a  test  tube  with  about 
100  drops  of  water ;  this  being  divided  in  two  parts,  the  one  is 
examined  with  some  drops  of  the  retained  zinc-sulphate  solution, 
the  other  with  the  barium  sulpho-phenate  solution.  If  any  re- 
action ensues  in  either  case,  the  one  or  other  of  the  retained 
solutions  has  carefully  to  be  added  to  the  bulk  of  the  solution,  in 
order  to  accomplish  the  exact  decomposition.  A  slight  excess  of 
zinc  sulphate  should,  however,  prevail,  so  that  the  barium  may 
be  completely  precipitated. 
Finally,  the  filtered  solution  of  zinc  sulpho-phenate  is  evapo- 
rated under  continual  stirring  until  a  drop,  when  allowed  to  fall 
on  a  cold  glass  plate,  congeals  to  a  salt  mass.  The  liquid  is 
then  allowed  to  cool  under  frequent  stirring,  and  the  resulting 
salt  mass  is  dried  in  a  w^arm  place.  When  completely  dry  it 
forms  a  white  salt. 
The  evaporation  of  the  solution  of  the  barium  sulpho-phenate, 
its  re-solution  and  the  filtration,  are  only  required  when  a  phenol 
